Pennethorne, John; Robinson, John [Ill.]: The geometry and optics of ancient architecture: illustrated by examples from Thebes, Athens, and Rome (London [u.a.], 1878)

THE APPAKENT PBOPOBTIO^S, 67

In this example the mass of the Portico is enclosed within an exact square, the Upper
Step being equal to the whole height, the same as in the first given quantities of a tetrastyle
Ionic Portico; also the whole height of the Entablature is within a fraction of \ of the height
of the Portico, the same as in other examples of the Ionic order. All the details of this small
Portico are beautifully designed and executed, but I do not possess sufficient materials of my
own collecting to enable me mathematically to lay down the curves and ornaments.

PLATE IV.

THE NORTH PORTICO CORRECTED.

This is a very perfect design, laid down and corrected to suit the given point of sight
with the same care as the Parthenon, but the Plate requires no explanation beyond what it
contains, as it is only a repetition of previous examples.

Fig. 1. The plan of the North Portico with the elevation of the same and of the return side
traced upon the three rectangular planes XY, XZ, YZ, passing through the point
of sight 0. In this example there is found to be a slight variation from the given
general proportions of the Ionic order. The whole height being divided into 12
parts, then the height of the Steps = 1 part, the Entablature = 2 parts, and the
Column = 8f parts instead of 9 parts.

Fig. 2. The detailed plan of the projections.

Fig. 3. The apparent length and breadth of the Middle Step.

Fig. 4. The angle of the Portico nearest to the point of sight 0, fixed in position upon the
vertical plane HOZ.

Fig. 5. The corrected design trigonometrically calculated upon the plane HOZ.

The Vertical Corrections obtained by Calculation.

Column. Entablature. Steps. Pediment.

No. 3 Design ... — 0*26 ... — 0'358 . . . + 0-23 ... — 024.